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Abstract

Although the vestibular system clearly plays an important role in the control of locomotion,
it is not clear to what extent it is also involved in the perception of our own locomotion. We
investigated whether vestibular information is used for the perceptual estimation of one’s own
walking speed. If vestibular information is used, perceived walking speed would be expected
to be lower during walking in place on a treadmill than when walking at the same speed across
the ground, as the forward acceleration of the head during walking is largely absent. To experimentally
address this hypothesis, we used a circular treadmill setup, consisting of a large
turn table (diameter 3.5m) and a motorized handlebar. Both could be actuated independently
from each other. In this setup, walking behind the moving handlebar on the stationary treadmill
stimulates both the otholiths and the semicircular canals, whereas this vestibular stimulation is
much reduced when walking in place on the rotating treadmill. The biomechanical information
is largely equal in these two conditions. Subjects had to judge their walking speed in a 2IFC
task. In one interval, they walked around the stationary treadmill behind the moving handlebar
at one of three standard speeds (31.7, 42.3, and 52.8 deg/s at a radius of 1.28 m, corresponding
to tangential speeds of 0.71, 0.94, and 1.18 m/s, respectively). In the other interval, they
walked in place at one of nine test speeds. Their task was to indicate in which of the two intervals
they walked faster. Accelerations (20–30 deg/s) as well as the duration of the walking
period (3–4 sec) were randomly set for individual intervals. A psychometric curve was fitted to
the speed judgments for each standard speed, from which the PSEs were estimated. The results
were in general agreement with the hypothesis. Subjects tended to underestimate their walking
speed when walking in place relative to actually walking around. This underestimation, however,
seems to be dependent on walking speed and varies considerably across participants. In
conclusion, vestibular information is used for estimating perceived walking speed.